Lithographic printing process



Oct. 4, 1955 c. L. BOTTHOF ET A1. 2,719,481

LITHOGRAPHIC PRINTING PROCESS F16. rif.

flaw/ma Pouf@ @WiWi/wa P4472' m MM United States Patent C LITHOGRAPHC PRINTING PROCESS Charles Laury Botthof, Kenilworth, Herman J. Schultz,

Glenview, and Olin E. Freedman, Chicago, Ill., assignors, by mesne assignments, to Direct Image Offset Corporation, Evanston, Ill., a corporation of Illinois Continuation of abandoned application Serial No. 239,416, July 30, 1951. This application July 29, 1954, Serial No. 446,448

5 Claims. (Cl. IUI-149.2)

This application is a continuation of our application entitled Lithographie Printing Process, bearing Serial Number 239,416, filed July 30, 1951, now abandoned.

This invention relates to the graphie arts and particularly pertains to improvements in lithographie printing processes.

For many years prior to the improved process herein disclosed, press or printing plates for lithographie presses have been most commonly produced of metallic sheets preferably of zinc or aluminum. These plates were proeessed to produce a grained surface having characteristics enabling the image substance to firmly adhere to the grained surface and enabling the non-image areas of the grained surface to retain suflcient moisture to repel greasy ink and thus keep the plate clean.

The most widely employed practice is to place the work or image upon the plate photo-mechanically either by the albumin process or by the deep-etch process, both of which are well known.

Briefly, the albumin process contemplates coating the plate surfaces with an albumin solution containing arnmonium bichromate. The Work is exposed on the plate through a negative and the coatings on those areas which are exposed to the light (the image areas) become insoluble in water, while the coating on the unexposed areas (the non-image areas) remains soluble. Thereafter the solution or coating which remains soluble is washed off and the` surface from which it is removed becomes receptive to water, while the areas coated by the insoluble solution remain on the plate surface and are receptive to ink.

Basically, the deep-etch method is similar with the exception that the exposure is through a positive instead of a negative, and the ink receptive image areas are slightly etched by application of a mordant such as ferrie chloride to somewhat flatten the graining over such areas.

In that the plates produced by the albumin process have a base of ammonium bichromate and albumin underlying the image substance in the image areas, water may attack such base from the marginal edges of the image areas to the detriment of sharpness and opacity of reproduction. Plates produced by the deep-etch process not only lack this disadvantage but possesses the advantage that the image areas are very slightly but evenly depressed with respect to the non-irnage areas due to partial removal of the graining in such image areas by etching, as previously discussed.

Naturally, during the production of these prior metal plates, they must be processed with additional well-known minor steps, such as counter-etching with weak acid and coating with gum arabic or other gum to make the non-image areas more receptive to water and more repellent to ink. Also, it is common practice to apply asphaltnm or lacquer to the image areas to increase the productive life of the plate.

Obviously, the plates produced by the above methods are capable of use in either direct or offset printing. It is well accepted that the production of these prior press 2 ,7 1 9 ,48 l Patented Det. 4, 1955 plates is costly from the standpoint of the cost of the materials from which they are produced and the cost of the eight to ten separate steps in the process of their production for use, as well as from the standpoint of the investment in equipment necessary in the photomechanical` processes of producing the plates.

Prior attempts have been made to produce low cost direct image lithographie plates. These attempts have been unsuccessful due, mainly, to unacceptable reproduction, loss of printing ability of plates after a comparatively few impressions, failure of the plates due to distortion and stretching, and prohibitive cost.

It is the principal object of the present invention to improve lithographie printing processes to enable a great and considerable reduction in the cost and time of produeing lithographie press plates without any sacrifice of sharpness and opacity of reproduction, the speed of the press using the plate, the productive life of the plate, or other essential characteristics of lithographie press plates.

The invention is exemplified in the following description and illustrated by way of example in the accompanying drawings, in which:

Fig. l is an enlarged diagrammatic illustration in cross section of a plate constructed for use in practicing our invention.

Fig. 2 is a diagrammatic illustration of the manner in which the image areas are depressed into the plate and the plate is embossed by such impression.

Fig. 3, diagrammatically illustrates the manner of deembossing the plate or returning the irnage areas to a normal printing plane from their depressed position.

The press plate construction To practice the present invention, it is essential to provide a laminated plate structure consisting of a lamina of metallic foil and a backing lamina of strong paper or card stock. The metallic lamina is preferably of aluminum foil from one to four thousandths of an inch thick, although any other metallic foil having the characteristics of aluminum foil which are essential in the present process may be used. Likewise, the above dimensions of thickness are given as an example in that the foil may be of a thickness other than that specified, if so desired.

The backing lamina is preferably of a strong tag stock suitably waterproofed by impregnation or coating. The backing lamina is preferably from two to twenty thousandths of an inch in thickness. Obviously, other substances may be substituted for paper or card stock as the backing lamina as well as other thicknesses employed, just so long as the backing has the characteristics essential in the present process.

The plate produced as above described is, of course, impervious to or resistant to the penetration of moisture in the amounts to which it may be subjected in use in ordinary lithographie processes. Likewise, it is suflieiently pliable or flexible that it may be mounted on the plate cylinder of a press.

Grainng It is necessary, 0f course, that the Working surface of the metallic lamina of the plate be grained in order that it will have an affinity for ink and water. This graining is accomplished by dry sand-blasting the working surface to obtain an even, uniform grain. This grain is finer than the smallest half-tone dot or the finest line it is desired to produce, so that smooth, unbroken reproduction of iine screen and line work will result. The grain, however, is of suicient depth to enable it to hold adequate water in the non-image areas to keep the plate clean.

This process of graining by dry sand-blasting leaves the4 grained surface free of oxidized metal, grease or foreign substances so that counter-etching with weak acid is ordinarily unnecessary. All that is usually necessary is to lightly airblast the surface to remove any residue of the sand-blast and:l the plate is ready for use. However, under some circumstancesv counter-etching in the usual manner may be employed.

Placing the work on the press plate To place the work upon the grained surface of the plate, a relief form of the material or image is made up asv for letter-press printing. The relief surface of the form is uniformly inked with a greasy ink coating of proper thickness. It is preferable that the ink be entirely free from chemicalV dryers which would tend to harden or glaze the ink to an extent that it would repel rather than attract additional ink.

When so inked, an impression from the relief surface of the form is made upon the grained surface of the plate. This impresses the relief surfaces of the form into the grained surface in excess of a thousandth of an inch below the printing plane of the grained surface of the plate and deposits an ink film approximately one-half the thickness of the ink film on such relief surfaces into the depressed image areas. The impression upon the press plate can be made in an ordinary letter-press proof press, a cylinder or a platen type printing press.

In order that areas, type characters, halftone dots, etc., which are to be placed upon the press plate may transfer a full and satisfactory film of ink which will result in satisfactory sensitization of the plate and make it completely receptive to ink, a rm impression, with adequate printing pressure in accordance with the well known methods of letter-press printing, is essential. This impression necessarily disposes the image areas somewhat below the normal printing plane; possibly to a depth of .0015 inch below the grained surface of the plate as an average. However, it is obvious that the impression will not dispose the image areas at a uniform distance below the grained surface of the plate because even with timeconsuming, expensive make-ready methods, it is impossible to limit the depth of such embossing of the plate to .0015 inch. Particularly in the handling of halftones and reverse or solid plates of comparatively large area, the relieving of impression at the edges and building up of impression (or pressure) over the interior portions to correct the phenomenon known in the industry as bearoff may well necessitate differentials of impression (or pressure) ranging through as much as .007 inch.

In Fig. 2 of the drawings, we have diagrammatically illustrated what we have termed the embossing of the plate effected by impression of the image areas therein, and obviously such impressions and embossing will remain due to the ductile quality of the metallic lamina and the deformable character of the paper backing.

After the impression is made, the plate is either permitted to stand a short period or is subjected to a warm atmosphere to set the ink on the image areas. Of course, the setting may be accelerated by the application of talc. The setting of the ink is to a point short of the point where the grease content of the ink hardens to a degree that it loses its affinity for additional ink. The setting, however, must be sufficient to remove most of the volatile solvent content of the ink.

When setting has been effected, the grained surface of the plate is treated to make the non-image areas more receptive to water and more repellent to ink. This is accomplished by the separate or simultaneous application of a weak acid and gum arabic or equivalent substance. The gum is spread uniformly over the grained' surface ofthe plate to provide a coating which is soluble in water, but notin hydrocarbony or similar solvents. The gum adheres to all metallic areas of the plate, but not the inkcoated image areas. Thereafter, by use of a suitable solvent, the ink may be washed out of the image areas.

As inwell known practice, the inked image areas may be= underlaid with asphaltum or lacquer to form a more permanent printing area where extremely long runs are contemplated.

After the press or printing plate has been so prepared and processed, the depressed image areas are restored to a proper printing plane relative to the non-image areas of the grained surface. This can be accomplished by a swaging action. Excellent results have been obtained by passing the plate between swaging members as illustrated in Fig. 3 of the drawings. It has been found that by such practice, they depressed image areas are restored or repositioned at a proper printing plane at the grained surface, Other methods of accomplishing the latter effect could be employed if desired.

Due to the fact that the impression of the relief form surface into the grained surface is in an amount in excess of the graining depth, the grain will be flattened in the image areas to obtain an effect somewhat like that obtained by the deep etch process.

By impressing the image area to a depth below the. normal printing plane thereof and then restoring the image area back to the normalV printing plane, important results are accomplished, chiefly among which is the fact that proper sensitization of the plate is effected, and, secondly, elimination of the time-consuming, expensivemake-ready operation of the locked-up form is effected.

By our process it is only necessary that matter in a form (type, mounted cuts, etc.) is reasonably uniform in height-to-paper, certain areas (particularly edges of halftones or reverse plates) may emboss as far as some .007 inch below the surface of the plate and then, without detectable distortion, be restored to the proper printingv plane (about .0005 inch below the top of the grain) through the debossing or disembossing or restoringl step as herein described.

Thus, in view of the ability to correct the plane of impression uniformly and quickly, the embossing of the plate at the time of making the relief impression becomes desirable, affording uniform and complete coverage of the sensitizing ink and permitting the elimination of costly make-ready time. We also point out that variations in the thickness of the laminated foil plates, normally ranging through fully .O02 inch, present no difficulties.

Uniformly excellent results have been achieved by use of such plates. That is to say, the reproduction from such plates is smooth and unbroken as well as sharp and uniformly opaque on papers of wide variety, even newsprint.

It has been found that the plate will retain its full eficiency throughout exceedingly long runs.

After the plate has been completely prepared, it may be employed to perform all of the functions hitherto performed by prior metallic plates made by prior methods.

Obviously, the original cost of the plate is but a fraction of the cost of prior zinc and aluminum plates. Likewise the process of placing the work upon the plate and preparing the plate for use is simpler, and greatly less timeconsuming and, consequently, much more inexpensive than prior methods. Further, no equipment or materials of the type so necessary in photo-mechanical processes are required in this improved process, thus further reducing plate production cost.

While the improved process has been described indetail herein, it is obvious that various changes may be made therein by those skilled in the art without departing from the spirit of the invention as defined in the appended claims.

Having thus described my invention, whatwe claim and desire to obtain by Letters Patent is:

l. In a process of producing a lithographie printing plate, the steps of providing a laminated plate of a lamina of deformable backing materiah, aI lamina of metallic foil having an exposed printing face, impressing an inked relief surface into said printing face to create an inked image area at a distance inwardly of the plane of Said face beyond a proper printing plane relative thereto and thereby forming a set indentation of the image area in the foil lamina and the backing material and correspondingly embossing the backing material in relief at its exposed surface opposite the printing face of the foil lamina, thereafter applying an external force to said plate to deemboss the backing material and force the indented inked image area of the foil lamina to a uniform printing plane relative to the printing face of the foil lamina.

2. In a process of producing a lithographie printing plate, the steps of providing a laminated plate of a lamina of a backing sheet of paper-like material and a lamina of relatively thin metallic foil having an exposed surface, impressing an inked relief surface into said exposed surtface to create an inked image area at a distance inwardly of the outermost plane of the exposed surface and beyond a proper printing plane relative thereto and thereby forming a set indentation of the image area in the foil lamina and the backing sheet and correspondingly embossing the backing sheet in relief at its exposed surface opposite the foil exposed surface, thereafter applying an external force to said plate to de-emboss the backing sheet and force the indented inked image area of the foil lamina to a uniform printing plane substantially at the foil exposed surface.

3. In a process of producing a lithographie printing plate, the steps of providing a laminated plate of a lamina of a backing sheet of deformable material and a lamina of relatively thin metallic foil having an exposed surface,

impressing an inked relief surface into said exposed surface by means of an inked unyielding relief form to create an inked image area in the exposed surface of the foil lamina with substantially all of said image area disposed inwardly of the outermost plane of the exposed surface unequal distances inwardly in excess of a proper printing plane relative thereto and thereby forming a set indentation of the inked image area in the foil lamina and the backing sheet and correspondingly embossing the backing sheet in relief at its exposed surface opposite the foil exposed surface, thereafter applying an external force to said embossing to de-emboss the backing sheet and force the indented inked image area to a uniform printing plane relative to the foil exposed surface.

4. The process of claim 3 in which the metallic foil is of a thickness of the order of between .001 to .005 of an inch and the backing sheet is of a thickness of the order of between .004 and .012 of an inch and wherein the inked image area is indented into the plate by the relief form in the order of between .0003 to .007 of an inch.

5. The process of claim 4 in which the inked image area is forced to a plane with the exposed surface of the ink thereon in substantially the same plane as the exposed surface of the foil lamina.

References Cited in the le of this patent UNITED STATES PATENTS 1,100,584 Tryon et al June 23, 1914 1,149,974 Chisholm Aug. 10, 1915 2,048,964 Osborn July 28, 1936 2,104,126 Hagelin Ian. 4, 1938 2,216,594 Marchev Oct. 1, 1940 2,276,594 Rowell Mar. 17, 1942 2,302,669 Batcheller Nov. 24, 1942 2,311,047 Hagelin Feb. 16, 1943 2,344,510 Hagelin Mar. 21, 1944 2,503,679 Newman Apr. 11, 1950 2,516,222 Linkmark July 25, 1950 FOREIGN PATENTS 17,647 Great Britain Aug. 28, 1897 204,517 Germany May 29, 1907 

